A typical vane-type camshaft phaser for changing the phase relationship between a crankshaft and a camshaft of an internal combustion engine generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil is selectively supplied to one of the advance and retard chambers and vacated from the other of the advance and retard chambers by a phasing oil control valve in order to rotate the rotor within the stator and thereby change the phase relationship between the camshaft and the crankshaft. A supply check valve is typically provided in order to prevent oil from flowing back to the source of the engine oil. It is also common to include a lock pin which is selectively engaged and disengaged with a lock pin seat. When the lock pin is engaged with the lock pin seat, rotation of the rotor relative to the stator is prevented. Conversely, when the lock pin is disengaged from the lock pin, rotation of the rotor relative to the stator is permitted based on input from the phasing oil control valve. One such camshaft phaser is described in U.S. Pat. No. 6,772,721 to Gardner et al., hereinafter referred to as Gardner et al. While the camshaft phaser of Gardner et al. may be effective, it may be difficult to implement the check valve within the rotor as taught by Gardner et al. In order to achieve compactness and simplify oil passages, it may be desirable to implement the check valve within the valve spool.
What is needed is camshaft phaser which minimizes or eliminates one or more the shortcomings as set forth above.